Angry Wasps Capture Intruding Ants, Fly Away, Airdrop Them

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What's a wasp to do when ants are ruining its picnic? Pick the
little pests up and airdrop them out of the way, according to a
new study.

That's the strategy of the
common yellow jacket wasp when competing with ants for food,
researchers report today (March 29) in the Journal of the Royal
Society Biology Letters.

The wasp, also known as Vespula vulgaris, is native to
the Northern Hemisphere, but has invaded temperate areas in the
Southern Hemisphere, including New Zealand, where the
drag-and-drop behavior was observed.

This is the first time wasps have been seen physically relocating
ants in an attempt to compete for food, said study author Julien
Grangier, a postdoctoral fellow at Victoria University of
Wellington in New Zealand. The unexpected flight, which leaves
ants confused but usually unharmed, also reveals the invasive
wasps' cleverness, Grangier said.

"Our results suggest that these wasps can assess the degree and
type of competition they are facing and adapt their behavior
accordingly," Grangier told LiveScience.

Ant vs. wasp

Ants and wasps battle relatively frequently, said Robert Jeanne,
an entomologist at the University of Wisconsin, Madison, who was
not involved in the study. Wasps have even been seen picking up
and dropping ant scouts that show up near nests looking to snack
on wasp larvae, he said. But those are defensive — not
competitive — behaviors. [Read: How to Eat
Ants Without Getting Bitten ]

The South Island of New Zealand is a hot spot for the invasive
wasps. In the forests on the island, aphids and other tiny
insects feed on beech tree sap. These bugs have little use for
the sugars the sap contains, so they excrete those sugars as a
sticky liquid called honeydew. Ants and wasps, on the other hand,
love honeydew.

Grangier and his colleagues wanted to understand how the
invasive wasps compete with native ants for food. So they set
up cameras at 48 stations baited with canned tuna (since protein
is in shorter supply than sugar in the honeydew-rich forests).
All but three of the stations attracted both wasps and ants.

Ant airdrops

Over the course of the months-long study, ants and wasps crossed
paths more than 1,000 times. Most of the time, the two species
quickly went their separate ways. But in a quarter to a third of
cases, the interactions were far less civil.

"The first surprise was to see that despite being 200 times
smaller, the
ants are able to hold their own by rushing at the wasps,
spraying them with acid and biting them," Grangier said. "But the
most amazing was to observe that wasps, apparently frustrated by
having to compete with ants, will pick them up in their
mandibles, fly off and drop them away from the food."

The researchers saw the involuntary ant flights 62 times at 20
different bait stations. The wasps didn't bother to take
the ants far, usually dropping them only a few centimeters
from the tuna. But that was enough. About 47 percent of the time,
the discombobulated ants never made it back to the tuna. Even
when the ants did make it back, the wasps beat them there 75
percent of the time.

If the ant-dropping was explained by competition, Grangier said,
it would increase when the food was in shorter supply. The
researchers watched the videos frame-by-frame, counting the
number of ants and wasps present during the airdrop episodes.

"We found that, as the number of ants on the food increases, so
does the frequency of ant-dropping and the distance the ants are
taken," Grangier said. "Our results thus show very clearly that
by dropping ants away, these wasps try to facilitate their access
to the food resources and to gain more for themselves, and they
do it in a very effective manner."

Unwanted insects

The wasps could try to kill the ants, but relocating them is
probably a safer option, Jeanne said. For one thing, he said,
"there's not a lot of meat on an ant," making them useless as
wasp prey. And then there's the tendency of the native New
Zealand ant (Prolasius advenus) to spray attackers with
an acidic chemical cocktail.

"If the wasp was to bite into an ant to crunch it and kill it, it
would probably get a mouthful of some of these compounds," Jeanne
said. "It wouldn't be a pleasant experience."

Although the wasps are all over the globe, he said, these
airborne food competitions seem to be unique to New Zealand. That
may be because wasps are so abundant in the beech forests there
that food competition has become
particularly cutthroat, Jeanne said.

So far, attempts to beat back the invasive wasp have been
unsuccessful, Jeanne said, but understanding the competition
between species could help.

"The more we know about the behavior of an invasive species or
interactions with other species like this, the more likely we are
to find an Achilles heel," Jeanne said.